Pipe couplings have been in service since the dawn of the industrial age, and hundreds of different designs are known. There is no best coupling for all purposes, so users must choose the features required for a particular application, and then choose the lowest cost coupling meeting those specifications. The variables are many: diameter, diameter variability, degree of sealing required, fluid being transferred, hydraulic pressure, exposure to the outside or not; removable or permanent weight limitations, space limitations, ease of installation and other factors all of which influence the selection of a coupling.
Preventing spillage of liquids is the primary requirement, important not only because of the high cost of some liquids, but also for preventing pollution of beaches, water reservoirs and inhabited areas. Even drinking water is becoming a valuable liquid and leakage thereof is no longer tolerated today as it was in the past.
The present inventors have disclosed and received patents on many design variations, relating to removable band-type couplings for large (over 75 mm) diameter pipes where sealing is required.
The present invention is also intended for large diameter pipes. With regard to pipe diameters under 75 mm, standard conventional methods using flanges and/or screw threads are satisfactory. Furthermore there are many special designs, for example swage lock systems, which are cost-effective for small copper tubes, the coupling being of moderate weight.
Sealing elements are widely used in industry, chemical processes, vehicles and almost everywhere that a fluid is transported in a pipeline. Drain lines which are usually not under pressure are also fitted with seals. Most smaller seal elements are available off-the-shelf and large sizes or special designs can usually be quickly manufactured to order.
It is known that when a seal element is in use and is subjected to the high pressure of the fluid being transported there is a tendency for the seal to bend outwards and thus allow spillage of the fluid.
Flexible seal members are used primarily for pipe joints, and the assembly of gauges, filters, flow controllers valves, sealing of broken pipes and the like
With regard to the sealing lip being pushed outwards, there are two approaches which are used to solve this problem. All known openable couplings have an opening range of up to 10 mm.
The metal outer casing, in which the seal element is housed or the metal band which is used to apply pressure to the seal, is made in a manner closely restraining the seal form, or at least supporting the seal lip in contact with the pipe. Such a design cannot be used where a pipe is curved or where there is some variation of pipe outer diameter.
The seal can be balanced by providing channels for the seal to be exposed to line pressure on both sides of the seal lip. This prevents seal failure but raises considerable complications, such as difficult and costly machining tasks arise as is seen in following examples.
The following US patents were found which illustrate the complexities of prior art balanced pressure sealing systems. Many of the designs require the drilling in metal of long small-diameter passages for a fluid, sometimes even at an angle other than 90° to the surface, generating a difficult machining task.
Pressure-balanced seal arrangements are seen in U.S. Pat. No. 3,961,798 to Damratowski et al., U.S. Pat. No. 4,327,921 to Reinsma et al., U.S. Pat. No. 4,557,489 to Wentworth, U.S. Pat. No. 4,813,692 to Hailing et al., U.S. Pat. No. 5,080,183 to Schumacher et al., U.S. Pat. No. 5,662,335 to Larsen, U.S. Pat. No. 5,890,881 to Adeff and U.S. Pat. No. 5,988,281 to Douglas et al. All prior-art arrangements require extra machining of metal, some needing special tools and equipment for manufacture. The most pertinent prior are is applicant's patent IL 121796 describing a seal adapted to be used with pipes of different diameters. However, this one was found not satisfactory in some cases with large diameters.